1. Field of the Invention
The invention relates in general to a method and device for preventing piracy of video material from theater screens and in particular to a method and device for preventing videotape piracy of material from theater screens by varying the frequency of the frame rate of a movie projector.
2. Description of the Prior Art
A frustrating problem in the movie industry is the pirating of first release films for the video tape market. In the movie industry, maximum profit is obtained by the use of xe2x80x9crelease windows.xe2x80x9d The essence of these release windows is to first release a film in first run theaters in the U.S. and then in succession second run theaters and various foreign markets, then to the airlines as in-flight movies, video tape and finally cable television. Movie pirates, however, frustrate the use of these release windows by entering a first run theater, videotaping the movie screen and then releasing pirated versions of the first run film on videotape to the public. This obviously causes substantial financial loss to the movie industry.
In a typical film based projection system the film is projected one frame at a time at 24 frames a second. Each frame has the projecting light flashed through the entire cell (that is all of the video lines are available all of the time). In reality the light is flashed at 48 times a second (twice on each frame). This is to avoid flicker perceptible to the human eye.
Video cameras scan very close to 30 frames a second with interlace (odd lines and then even lines.) Video cameras integrate light much the same way as the human eye does, but in fact video cameras have superior integration abilities. Accordingly alterations to a movie that will confuse the image for a video camera will typically render the image unwatchable to the audience.
When a video camera is used in a movie theater, the scanning of the light on the screen is easily recorded on video tape because the lines are available all of the time, the frame rate of the video camera is slower than that of the projector and the camera has excellent integration facilities.
Future cinemas will become electronic and movies will be projected via electronic projectors. These electronic projectors will most likely received digitized video. Examples of these projectors are digital light modulators (DMD""s), liquid crystal displays (LCD""s) and plasma devices. (U.S. Pat. No. 5,079,544 and U.S. patent application Ser. No. 08/495,290 describe DMDs and are hereby incorporated by reference.) In all probability the projectors will be progressive scan projectors (non-interlaced) which progressively scan a frame at 24 frames a second as before (an effective frame rate of 48 frames a second). However, even if future cinemas use interlaced scan projectors, where the image will not be flashed all at once but instead scanned line by line or by groups of lines much like a television display, if such images are video taped, only a minor distortion in the video tape occurs. It is similar to when a video tape is made of a television that is on, there is always a distortion of that image because the two scanning frequencies are not synchronized. Movie piracy by video tape still remains a problem with interlaced projectors because this distortion is easily removed by synchronizing the video camera to the frame rate of the projected video. As movie pirates are becoming increasingly more sophisticated, a better way of preventing piracy is needed.
Accordingly it is an object of the invention to prevent the piracy of movies in a movie theater when the movie is being displayed by an electronic projector. This object is achieved by changing frequently the frame rate of the projector. A relatively small adjustment of both increasing and decreasing the frame rate of the projector is not noticed by the viewers but causes synchronization problems for the pirate video camera operators.
When the frame rate is varied frequently it has the effect of constantly updating the synchronization problems of the bootleggers camera. Typically the integration rate is set on a video camera for a particular frame rate of the projector. If the frame rate is changed the integration must be changed manually. If the frame rate is changed frequently the integration must be changed frequently and synchronously, which is almost impossible to accomplish manually. The human eye adjusts its integration ability on a real time basis, therefore, the changing frame rate is not noticed by the human eye, yet it causes distortion in the video camera image. The resulting distortions on the bootleggers video tape if the bootlegger cannot keep up with the changing frame rate on a real time basis, are beat frequencies for the scenes being displayed at a reduced frame rate than the frame rate of the video camera and blurring of rapidly moving objects for scenes projected at the faster frame rate.
It is a further object of the invention to change the frame rate of the projector in a non-predictive manner such as by a cryptographically secure pseudo-random number generator or a natural source generator. This prevents the pirate from simply adjusting the video camera in a predictive manner to accommodate a predictively changing frame rate frequency.
It is yet another object of the invention to prevent piracy of a movie which has a changing frame rate when the pirate simply uses a slower frequency than any of the frame rates of the projector. This object is achieved by displaying scenes that contain slower motion at a reduced frame rate and scenes that contain rapid motion at an increased frame rate. The pirate""s choice of a low frequency will then cause blurring of the rapidly moving objects in scenes projected at the faster rate.
In yet a further object of the invention, the frame rates of the scenes with slower motion are varied within a reduced frequency range, while scenes that contain high speed motion are varied within an increased frequency range.
It is yet even another object of the invention to vary the line rate of the projector and/or the pixel rate. These alterations will also cause distortion to the video camera operator.
It is yet even a further object of the invention to provide scene tags which indicate scenes that are to be displayed at slower frame rates and scenes that are to be displayed at faster frame rates. These scene tags are provided within the video stream after editing of the film and detected by the projector.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.